A typical wireless receiver has several gain stages in a radio frequency (RF) chain to enhance the received signal so that a receiver analog-to-digital converter (ADC) can digitize the signal of interest (of the receive signal) with sufficient integrity to allow for digital processing to demodulate signal(s) of interest. Typically, there is an automatic gain control block that measures the ADC output and accordingly adjusts the RF/analog gain settings to ensure a certain target signal level at the ADC input (which typically provides a tradeoff between minimizing saturation and minimizing quantization error).
Generally, it is advantageous to use higher gain settings in receiver chain blocks such as the LNA (low noise amplifier) that are located at the beginning of the RF chain versus the gain blocks such as the VGA (variable gain amplifier) at the end of the chain near the ADC. Such a configuration minimizes thermal noise and results in improved signal quality. However, if the LNA settings are too high, saturation can result and signal integrity is compromised. When there is no adjacent channel or out-of-band interference, the ADC output can be monitored to detect the likelihood of saturation. However, when there is adjacent channel interference, there may be saturation at the LNA and the subsequent analog low pass filters may then suppress the signal power resulting in a low signal measurement at the ADC output thereby preventing accurate detection of saturation.
It is desirable to have methods and apparatuses for selecting gain settings of receiver chains to alleviate distortion to receive signals due to saturation of components within the receiver chain.